This invention relates to a navigation device for a vehicle comprising a compass for measuring the orientation of the vehicle which includes means for deriving first orientation signals by regular sampling of the measured orientation, a measuring unit to determine the variations in the orientation of the vehicle and having means for deriving second orientation signals from regularly recorded samples of the said variation of the orientation, and a digital filter unit which filters received first and second orientation signals.
Such a vehicle navigation system is known from U.S. Pat. No. 3,630,079. In the known navigation system the orientation signals are combined by means of the filter unit to determine therefrom, with greater accuracy, the orientation along which the vehicle is moving. This latter orientation is then used to determine position coordinates of the vehicle. In this known navigation device a gyro compass is used to determine the first orientation signal and the second orientation signal is derived from velocities measured by means of the Doppler effect. The known navigation devices uses a computer which processes samples of the presented signals and weights the presented signals on the basis of their error margins.
A disadvantage of the known navigation device is that it is not very suitable for use in land vehicles such as for example, motorcars or trucks. In fact the cost of a gyrocompass and of a velocity measuring unit based on the Doppler effect are high as compared with that of the land vehicle.